Optional binary payloads in VM service events.

runtime/bin/vmservice/observatory/lib/service_io.dart

Index: runtime/bin/vmservice/observatory/lib/service_io.dart
===================================================================
--- runtime/bin/vmservice/observatory/lib/service_io.dart	(revision 39216)
+++ runtime/bin/vmservice/observatory/lib/service_io.dart	(working copy)
@@ -4,7 +4,9 @@
 
 library service_io;
 
+import 'dart:async';
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:observatory/service_common.dart';
 
@@ -40,6 +42,12 @@
   void close() {
     _webSocket.close();
   }
+  
+  Future<ByteData> nonStringToByteData(dynamic data) {
+    assert(data is Uint8List);
+    return new Future.sync(() =>
+        new ByteData.view(data.buffer, data.offsetInBytes));
+  }
 }
 
 /// The [WebSocketVM] communicates with a Dart VM over WebSocket. The Dart VM